It is often desired to manufacture articles out of plastic, both by hobby persons and large companies alike. Many times such production is required to keep the invention secret. In others, it is essential to make small runs and test the market, before hiring a large manufacturer for mass production.
In the past, there was a lack of affordable, capable, lightweight and safe plastic injection equipment.
The small machines currently in production, utilize custom manufactured parts driving up the cost. Since custom injection molding is a specialized trade, there is not enough demand to justify mass production of such equipment in order to lower the price.
The small equipment currently produced is inferior to large industrial injection molding machines, because of injection principle used. Currently produced small machines utilize stagnant heat technology to melt the plastic. Plastic is loaded in the barrel, and electric heater is utilized to melt the plastic before injecting. Since plastic is an insulator and does not conduct heat very well, plastic ends up being overheated. Such practice degrades plastic resins, reducing the quality of the part and inducing harmful fumes. Another affect of overheating the plastic is warpage created in injecting thicker parts, because of induced shrinkage while cooling from abnormally high temperature.
Small machines with higher capabilities utilize cast iron parts to withstand forces for generating higher pressure and clamping force. Such construction makes them prohibitively heavy to be moved and installed by one person. More importantly, common postal carriers cannot be used for shipment, requiring costly and inconvenient truck freight instead.
Besides inferior stagnant heat technology, some small machines also utilize air cylinders to increase pressure beyond what is possible to achieve manually. Such combination is very unsafe. Unlike incompressible hydraulic fluid used in large industrial machines, compressed air creates volatile pressure surge once released into air cylinder used for injection. This pressure surge is transferred to overheated and viscous plastic. In case of any error on the part of the mold maker or the operator, as well as machine failure, the molten plastic will violently squirt out. On the other hand, plastic will safely oozing out in the case of using lower temperature and incompressible injection fluid.